Oscar Riveros used JSR-331 to develop a Clojure-based environment for solving puzzles. You may read more in this manual “Constraint Programming with Puzzles“. All sources and examples are freely available from GitHub. I haven’t had a chance to check it myself (yet!) but any comments and suggestions are welcome. Thank you, Oscar!
This is a good trend as JSR331 allows creation of user-friendly domain specific APIs for constraint programming in different JVM languages.
Constraint Programming Standardization 